This invention relates to a method and apparatus for compression of waveform sampled data, and particularly to such a system for a digital data processor for a sampled video signal.
The customary method of sampling a waveform, such as a video signal for digital processing, does not take into consideration all of the data contained in a sample period for maximum fidelity of the sample data. Usually periodic point sampling is performed, often with an averaging effect due to the speed of the sampling circuit. This point sampling technique is commonly used for digital control of video display because the display is customarily comprised of a matrix of picture elements (pixels) arranged in rows and columns. For each pixel, all that can be encoded in digital form is one sample value. This is not adequate to yield maximum fidelity even if the sampling rate is at the Nyquist limit of 2 f where the essential frequency range of the video signal is limited to f cycles per second, i.e., even if the sampling (pixel) interval is the Nyquist interval of 1/2 f. In a practical application, the sampling rate is usually much less than the Nyquist limit of 2 f because of the limited number of pixels in the array, typically 265.times.265 or 512.times.512 pixels. It would be desirable to encode for pixel display a value which has more information about the signal during the pixel interval than just its amplitude at the sampling point in order to enhance the video display.